Re: Seeking a KVM benchmark

Paolo Bonzini
2014-11-10T17:28:34Z

On 10/11/2014 15:23, Avi Kivity wrote:
> It's not surprising [1]. Since the meaning of some PTE bits change [2],
> the TLB has to be flushed. In VMX we have VPIDs, so we only need to flush
> if EFER changed between two invocations of the same VPID, which isn't the
> case.
>
> [1] after the fact
> [2] although those bits were reserved with NXE=0, so they shouldn't have
> any TLB footprint

You're right that this is not that surprising after the fact, and that
both Sandy Bridge and Ivy Bridge have VPIDs (even the non-Xeon ones).
This is also why I'm curious about the Nehalem.

However note that even toggling the SCE bit is flushing the TLB. The
NXE bit is not being toggled here! That's the more surprising part.

Paolo